Tuning mechanism



Dec. 13, 1949 j J. E. TILLMAN 2,491,341-

TUNING MECHANISM I Filed Dec. 18, 1947 2 Sheets-Sheet 1 Inventor: John E.Till'nqan,

|-|is Attorney.

Dec. 13, 1949 J. E. TILLMAN TUNING MECHANISM 2 Sheets-Sheet 2 Filed Dec. 18, 1947 Inventor: John E.Tillman, b Zz/za AM H is At't or-ney.

Patented Dec. 13, 1949 TUNING MECHANISM John E. Tillman, Phoenix, Ariz., alslflml' to Gen-' eral Electric Company, a corporation of New York Application December 18, 1947, Serial No. 792,589

1 Claim. (Ci. Id-10.7)

My invention relates to tuning mechanism and more particularly, to mechanisms employed for tuning resonant circuits such as those used in,radio transmitting and receiving apparatus. It is a primary object of my invention to provide improved tuning .means for such resonant cir-' cuits.

A particular object of my invention is to provide a tuning mechanism for radio apparatus which obtains a linear relationship between the frequency and the tuning drive.

A'further object of my invention is to provide means for tuning a radio receiver such that a linearly calibrated dial may be employed as an indicator of the receiver frequency.

A more specific object of my invention is to provide a permeability tuner, using constant" pitch coils and cylindrical iron cores, for radio apparatus and the likewhich obtains a linear relationship between the frequency of operation and the position of the control knob.

The features of my invention which I believe to be novel are set forth with particularity in the appended claim. My invention itself. however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a fragmentary perspective view of a tuning mechanism suitably embodying my invention; Fig. 2 is a detail view of the spiral pulley member of Fig. 1; Figs. 3 and 4 are fragmentary side elevations of the actuating mechanism of the tuner of Fig. 1; and Fig. 5 is a fragmentary bottom view of the mechanism of Fig. 3. Like reference numerals indicate like elements in the several figures.

Referring to Fig. 1, there is shown in fragmentary form a tuning mechanism comprising a fixed supporting member .I and a sliding frame 2. Fastened to the supporting member I are one or more coil forms 3 on which are wound constant pitch coils 4 having suitable inductance and resistance characteristics. The sliding frame 2 is provided with an equal number of cylindrical compressed powdered iron cores or slugs 5 suitably positioned for insertion in the coil forms 3. Adjusting screws 8 are provided, by which means the iron cores 5 may be individually positioned with respect to the sliding frame 2. A guide member I is attached to the sliding frame 2. A support bearing, illustration of which is omitted in order to simplify the .drawing, is provided for the guide member I. A supporting member 3 is provided at one end of the guide member I, and

vided at the other.

I provide a conventional pulley-and-cord arrangement comprising a control knob ill, an indicating dial Ii, and three pulleys I2. l3, l4 mounted on parallel shafts i5, i6, II. The dial ii is provided with suitable linearly spaced indicia I 8. A cord IQ, of suitable length and hearing a pointer 20, is wound around the pulleys 12,

I3, M in the customary manner; cord tension is maintained by means of a spring 2| fastened between one end of the cord l3 and a nubbin 22 on the drive pulley l4. Illustration of the supporting bearings for the shafts l5, l8. I1 is omitted for the purpose of simplifying the drawing.

As means for varying the position of the slid' ing frame 2 with respect to the supporting member I, I provide a spiral-cut pulley member 23 mounted on the drive shaft H. A wire rope or other cord 24 is fastened at each end to the two members 8, 8 at the ends of the guide member 1. and is wound on the pulley member 23 in a manner to be hereinafter more fully described. By these means, the iron cores 5 are inserted in the coil forms 3 at a varying rate when the control knob I0 is rotated at constant speed. By winding the constant pitch coils 4 so that they comprise suitable inductance and resistance characteristics, a linear relationship between the coil inductance and the movement of the pointer 20 is obtained.

Referring to Fig. 2, there is shown the spiralcut pulley' 23 mounted on the drive shaft IT. The form of member 23 is essentially that generated when a wedge-shaped inclined plane is wound continuously about a cylinder. Thus the peripheral surface 25 follows a curve which is substantially that of an Archimedes spiral. The trans verse surfaces 26 are hereinafter referred to as the ramp surfaces, since these surfaces constitute the ramp of the aforementioned inclined plane. The peripheral surface 25 is undercut to provide a root or seat for the cord 24 against the ramp surface 26. The pulley member 23 is provided with a longitudinal hole 21. The cord 24 is wound continuously around the pulley 23, in such a way that the length of cord on the pulley is always constant. This is accomplished by winding the cord 24 around the peripheral surface 25 and through the hole 21 so that, on rotating the drive shaft l1, the cord 24 simultaneously winds in one direction and unwinds from the same surface in the other direction.

Fig. 3 shows the drive mechanism of the device of Fig. 1 with the cord 24 unwinding from the smallest diameter of the spiral-cut pulley. This position corresponds to the highest frequency tuning point of the associated radio apparatus. since the iron cores I (Fig. 1) are totally withdrawn from the coils 4. As the drive shaft i1 is rotated in a clockwise direction, the sliding frame 2 carrying the iron cores 5 (Fig. 1) is caused to move to the left, thereby progressively inserting the cores 5 in the coils 4 (Fig. 1) and decreasing the operating frequency. Thus, the cores I are inserted in the coils 4 at a varying rate while the pointer 20 moves at constant speed.

It will be seen that both ends of both portions of cord 24 wound on pulley 23, leave the spiral pulley member 23 at essentially the same point 28. Furthermore, one end of the cord 24 is fastened to a point 29 on the supporting member 8 which is in transverse and longitudinal alignment with the peripheral surface of smallest radius of the spiral pulley 23. The other end of the cord 24 is fastened to a point 30 on the supporting and adjusting member 9 which is in transverse and longitudinal alignment with the peripheral surface of the largest radius of the pulley 23. Thus, it is seen that the line of action of the cord 24, i. e. the straight line between points 29 and 30 along which force is applied to move frame 2, is fixed and always tangent to the peripheral surface 25 at a point 28 at which the cord leaves the pulley 23. The cord 24 also lies fiat against the ramp surface at the point of tangency 28. In other words, the developed locus of the peripheral surface of the pulley member 23 is substantially coincident with the line of action of the drive cord 24. By these means, the tension of the drive cord is maintained substantially constant throughout the travel of the sliding frame 2. The member 9 is bowed or bent inward, and the cord tension is adjusted by means of a screw 3| so that a firm frictional contact obtains between the cord and the peripheral surface of the spiral pulley 23.

Referring to Fig. 4, the sliding frame is shown in a position corresponding to the lowest operating frequency. It will be observed that in this position, cord 24 is tangent at a point 28 on the peripheral surface of largest diameter of the pulley 23.

Fig. 5 is a fragmentary bottom view of the mechanism of Fig. 3. This figure shows more clearly the transverse locations of the fastening points 29, 30 with respect to the pulley member 23. Fastening point 29 is shown in transverse alignment with a point 32 on the peripheral surface of smallest radius, and fastening point 30 is shown in transverse alignment with a point 33 on the peripheral surface of largest radius. Cord 24 always maintains a substantially straight line between fastening points 29, 30.

In summary, my invention provides simple and effective means for tuning radio apparatus over a band of frequencies. The advantages of inductance tuning are obtained, and linear dial calibration is provided without the use of variable pitch coil windings or specially shaped' tuning cores.

It will be seen that my invention provides simple means for converting uniform linear motion to a related nonuniform linear motion. In such an application, the uniform motion may be imparted to the cord l9, (Fig. 1), and the cord 24 may be attached to the member to which the desired nonuniform motion is to be imparted.

While I have shown a certain specific embodiment of my invention, it will be understood that numerous variations and modifications may be made without departing from the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

Apparatus for converting a given uniform linear motionto a related nonuniform linear motion comprising a first cable to which said uniform linear motion is imparted, a system of coplanar circular pulleys, said first cable being frictionally engaged on said pulleys, a drive shaft fixed on one of said pulleys, a pulley member of varying radius fixed on said shaft, a second cable continuously wound on said pulley member, a traveling member, the respective ends of said second cable being attached to spaced points on said traveling member positioned on opposite sides of said pulley member, said points being so located that the developed locus of the peripheral surface of said pulley member is substantially coincident with the line of action of said second cable, said second cable being in positive frictional engagement with said pulley member, whereby said nonuniform motion is imparted to said traveling member.

JOHN E. TILIMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,260,985 Benton et al. Oct. 28, 1941 2,286,283 Kirk et al June 16, 1942 2,370,714 Carlson Mar. 6, 1945 FOREIGN PATENTS Number Country Date 46,854 Add. France Aug. 4, 1936 

